What is the replica on fork Describe the DNA replica on mechanism star ng from the forma on of this structure Replication Fork at SV40 Ori 1 2 3 4 5 replica on fork transi on region b tw template DNA newly synthesized DNA moves 5 3 usually bi direc onal Large T an gen moves 5 3 as a DNA helicase unwinding the DNA crea ng the replica on fork RPA acts as a ss DNA binding protein on each of the 2 single strands preven ng re hybridiza on DNA primase DNA polymerase binds each single strand to synthesize RNA primer RF C clamp loader displaces DNA polymerase DNA primase from template RF C recruits PCNA sliding clamp which allows DNA polymerase to be processive synthesize leading or lagging strand complementary to single strands produced by replica on fork Lagging strand Which strategy is u lized to solve the over winding issue during DNA replica on PROBLEM Unwinding of DNA ahead of replica on fork produces torsional tension over winding SOLUTION SWIVEL is a topoisomerase that relieves over winding in DNA ahead of the replica on fork 1 2 Updated View of Orc Activation at S phase Describe the mechanism of ORC ac va on in the cell cycle In G1 Mcm Cdc6p Cdt1p are loaded ORI ORC Mcm2p Mcm7p bind Cdc6 and Cdt1 recruit an ORIORC activator of MCM to promote Mcm4p Mcm6p Mcm7p Initiation of fork movement Cdc6p must bind chroma n Cdt1p binds Mcm2p Mcm7p In S phase Cdc6p Cdt1p recruit Mcm helicase ac vator to promote ini a on of replica on fork BEFORE Cdt1p is recruited have helicase ac vity
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